Ensure cableless control reliability

Industrial wireless, or using ANSI’s term, cableless control, requires reliability. Don’t let radio frequency interference lead to downtime; follow these policing precautions.
By Dan Junker September 18, 2013

A cableless mobile control station can provide mobile industrial wireless control, allowing users full view of the equipment under control, such as this crane application. Courtesy: Automation Rangers Ltd.Prepare your manufacturing production area or facility for industrial wireless applications for control, or as ANSI now says, “cableless” control. Radio frequency (RF) interference can lead to downtime, but can be virtually eliminated if proper precautions are taken. Several significant solutions exist among certified ANSI “cableless control” manufacturers. Conducting an RF audit on a machine or process area follows the adage, “An ounce of prevention is worth a pound of cure.” Reducing or eliminating wireless interference can help keep your area shutdown free. Attention to the design of cableless control systems can help.

ANSI: cableless control

Cableless enabling pendant is secured to the user. Courtesy: Automation Rangers Ltd.Recently “Cableless Control” was adopted into the ANSI standards from NFPA 79-2012 and RIA R15.06-2012. Cableless control has long been recognized by the European Standards including ISO EN 10218, EN 13849-1, and EN62061. Wi-Fi and other uses for RF have been around for a long time and often are not considered critical. Basically, cableless control is wireless or remote control that is considered control reliable or fail safe. NFPA 79-2012 Cableless Control Functions 9.2.7 is a good start for the requirements necessary for a safe, reliable control system. “Cableless Control” controls until a fail-safe actuation of an e-stop or a signal failure. So it is important to make sure any possible interference is kept to a minimum, much the same as protecting against noise with proper electronics design.

“Cableless Control” is being applied in start-up, installation, testing, operation, and maintenance of machine and process systems. A cableless system should be easy to design, install, and operate with little in the way of maintenance necessary over its lifetime. Start with a basic cableless e-stop or enabling system. Once that is accepted, work your way up to a mobile control station as a good way to get everyone comfortable with the technology.

Many legacy systems are well over 10 years old. Cableless control systems are much more robust than typical standard wireless Ethernet switches or routers. “Cableless” devices or systems being applied are directly integrated into mission critical automation and safety systems. Many Fortune 500 and Fortune 100 companies and their original equipment manufacturers (OEMs) are starting to install these devices globally.

Assessing, auditing RF

A radio bus repeater helps ensure strong wireless signals where needed. Courtesy: Automation Rangers Ltd.Begin management of potential interference from RF devices or systems by auditing your plant environment for all radio frequency sources. A check list of items for an RF audit follows, along with what to document when installing an RF transmitter/receiver on-site. Standard design considerations for electromagnetic interference or radio frequency interference (EMI/RFI) are advised. Inexpensive RF spectrum analyzers are available through most RF system providers.

Most customers have not done this. Very few who do this have signal problems. One customer that did have an issue fixed it with a quick, easy manual adjustment to a new frequency. The reason for implementing an RF policing effort is that RF devices populate the environment more often, and regularly. At some point, unmanaged, they could become a problem. Obviously, addressing the potential for a problem now is better than dealing with an unknown problem that causes downtime later.

RF audit checklist

1. Device audit information necessary to build a RF write map for RF management.

a. “Cableless control” application:
i. New or retrofit?

ii. Interface to an existing or surrounding system?

iii. How many cableless devices in an area or facility?

iv. Control

1. Mobile control station

2. Pendant

3. Network

4. Device or instrument

v. Safety
1. Level of safety

2. Single or dual channel

3. Safety network

b. Manufacturer:

c. Model number:

d. Description or specifications:

e. Configuration:

f. Parameters:

g. If installed with software, get copy of file.

h. Operating frequency:

– Country (This is important because Europe and North America have different frequency ranges available for commercial use, so ensure the specification includes FCC-compliant equipment.)
i. Encryption:

j. FCC ID:

k. RF emissions:

l. RF power:

m. Operating range:

n. Antenna type and specification:

o. Antenna cable and specification:

2. Conduct a radio frequency scan of your facility.

a. Be aware, similar to electrical noise, RF may occur based on events and often is inconsistent, so a scan may need to be conducted for 24 hours or more.

b. Some manufacturers of RF equipment will scan your facility for you, but you may need to buy or rent a scanner to do a thorough longer-term analysis.

3. The easiest way to determine success for a device is to start with one unit and monitor on/off performance over a week or even a month. If the device never turns off, then you are reasonably sure you don’t have a conflict. This is how most customers do it.

Evaluation recommendations

1. Group the frequencies and determine if there are overlaps.

2. Determine if the technology overcomes the overlap. Frequency shifting technology will tolerate much greater population than standard units without shifting.

3. Determine the ability of the device or system to overcome RF interference. This will determine if a device will adjust to interference, if it needs its own band, or another design consideration. Look at:

a. Width of frequency signal (broad and flat versus narrow and sharp)

b. Manual frequency shifting

c. Automatic frequency shifting

d. Frequency-hopping spread spectrum

4. Component design for electronic based control systems should always be evaluated for EMI/RFI, and the proper designs for wiring, cabling, and termination should be followed to keep interference to a minimum.

Click to next page for an RF management strategy, followup, and RF reliability tip, along with more cableless photos, including a wireless e-stop.

RF management strategy

Yes, e-stops can be wireless, as this cableless control e-stop demonstrates. Courtesy: Automation Rangers Ltd.Strategies for management of your radio frequency environment are varied. One example is using the 30-900 MHz range for two-way radio, 902-928 MHz range for control, 2.4 GHz for wireless Ethernet communication, and monitoring inside and outside potentially invasive frequencies to protect against interference. For most applications this requires a small amount of documentation and awareness for system design. This has given birth to the term “RF Police.”

There is little related documentation online, so in many cases it is left up to common sense. There are many documents related to troubleshooting RF problems in an industrial environment, and they will give clues for strategies to prevent interference. Another reliable method for strategizing is to contact manufacturers of the RF-transmitting devices and ask what they suggest.

RF interference control tasks

To control RF interference consider these responses.

1. If RF interference occurs, then a procedure similar to addressing electrical interference needs to be put into action.

a. Interview all people using the area for knowledge of the use of a new RF device.

b. If that doesn’t turn up the problem, then bring in a RF scanner and try to identify the problematic RF device.

c. If the problem comes from an outside source over which you have no control, address the concern with a strategy that negates the problem.

2. If it is determined that there is potential for RF interference, then a course of action must be decided.

a. Contact the manufacturer for recommended solutions.

b. Contact the outside source if not under your control and ask it to filter the device.

c. Use filters to stop or limit transmission of transient RF.

d. Remove offending devices that do not have internal resistance built in.

e. Remove offending devices that are interfering with other devices.

f. Replace offending devices with newer technology that is either resistant or filtered.

3. Most reputable manufacturers offer solid solutions to limit device interference.

Following up

Mobile radios can be intermittent sources of radio frequency interference (RFI), demonstrating the need to police use of radio frequencies in the workplace. Courtesy: Automation Rangers Ltd.Re-evaluate and/or monitor to stay on top of the situation.

After addressing the RF conflict, deciding on the type of technology needed to accomplish control is no different than in any other control project. In general, here are the types of equipment available. Some devices are capable of integration with any system and others are proprietary to a manufacturer and do not play well with others.

1. “Cableless safe control” between PLCs or process control systems

a. Security?

b. Safety rated?

2. Data transmission or bus system? Safety rated?

3. There are systems that address I/O—discrete, safety, and analog. (Some are flexible; some are not.)

4. Mobile control stations (Most are flexible, but watch for the safety ratings, specifically single channel versus dual channel, or the ability to be part of a safety network.)

5. Pendants very similar to enabling pendants or crane control pendants. (Watch the safety rating and application.)

6. Devices like instruments or switches with a receiver monitoring their signal

All systems must have continuous communication with an ID, be one-to-one, and include redundant monitoring of third-party safety circuitry, communication link monitoring, battery monitoring and alarm, along with a method for swapping batteries without causing a stop. A few systems offer repeaters; security; displays; lighting; explosion-proof capability; a built-in safety bus; shock, drop, and roll detection; as well as vibration and audible alarms.

Frequent RF monitoring                                                                                       

A radio frequency spectrum analysis tool helps track local RF use, avoiding conflicts and maintaining reliability. Courtesy: Automation Rangers Ltd.Applications for RF control technology are part of our everyday environment; RF control quickly pays for itself. Elimination of radio interference will become as commonplace as troubleshooting a circuit. It starts with knowing what the environment contains.

A risk assessment performed by certified safety professionals will determine the value of “cableless control” versus other solutions. Many safety professionals do not have experience with “cableless control.”

The author thanks information contributors for this article: Jamie Sanderson at HBC Radiomatic; Stacy Shumpert at Procter & Gamble; Brian Rowell at Fluor Daniels, Lancaster, S.C.; Ted Sberna at White Horse Safety; Steve Leytus at Nuts About Nets; Mike Kunkle at MEK Consulting; and Brian Huber at Machine Safety Specialists.

– Dan Junker, electrical sales for Ohio, Automation Rangers Ltd. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering and Plant Engineering, mhoske@cfemedia.com.